Template matching on ibc merge candidates

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes processing circuitry. The processing circuitry determines an initial block vector for predicting a current block in a current coding tree unit (CTU) in response to the current block being predicted in an intra block copy (IBC) mode. The processing circuitry performs template matching based on the initial block vector to determine a refined block vector that points to a reference block in a same picture as the current block, and reconstructs the current block based on the reference block.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 63/239,767, “TEMPLATE MATCHING ON IBC MERGECANDIDATES” filed on Sep. 1, 2021, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Uncompressed digital video can include a series of pictures, eachpicture having a spatial dimension of, for example, 1920×1080 luminancesamples and associated chrominance samples. The series of pictures canhave a fixed or variable picture rate (informally also known as framerate), of, for example 60 pictures per second or 60 Hz. Uncompressedvideo has specific bitrate requirements. For example, 1080p60 4:2:0video at 8 bit per sample (1920×1080 luminance sample resolution at 60Hz frame rate) requires close to 1.5 Gbit/s bandwidth. An hour of suchvideo requires more than 600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth and/or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless compression and lossy compression, as well as a combinationthereof can be employed. Lossless compression refers to techniques wherean exact copy of the original signal can be reconstructed from thecompressed original signal. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is smallenough to make the reconstructed signal useful for the intendedapplication. In the case of video, lossy compression is widely employed.The amount of distortion tolerated depends on the application; forexample, users of certain consumer streaming applications may toleratehigher distortion than users of television distribution applications.The compression ratio achievable can reflect that: higherallowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding and/or decoding of spatially neighboring,and preceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is using reference data only from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode, submode, and/or parameter combination can havean impact in the coding efficiency gain through intra prediction, and socan the entropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (110) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Motion compensation can be a lossycompression technique and can relate to techniques where a block ofsample data from a previously reconstructed picture or part thereof(reference picture), after being spatially shifted in a directionindicated by a motion vector (MV henceforth), is used for the predictionof a newly reconstructed picture or picture part. In some cases, thereference picture can be the same as the picture currently underreconstruction. MVs can have two dimensions X and Y, or threedimensions, the third being an indication of the reference picture inuse (the latter, indirectly, can be a time dimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 2 , a current block (201) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (202 through 206, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry. The processing circuitry determines aninitial block vector for predicting a current block in a current codingtree unit (CTU) in response to the current block being predicted in anintra block copy (IBC) mode. The processing circuitry performs templatematching based on the initial block vector to determine a refined blockvector that points to a reference block in a picture as the currentblock, and reconstructs the current block based on the reference block.In some examples, the processing circuitry determines the initial blockvector based on a merge index included in a coded video bitstream. Themerge index indicates a block vector candidate in an IBC merge candidatelist including a plurality of IBC candidates in an IBC merge mode.

In an example, the processing circuitry parses, from the coded videobitstream, a first flag indicative of the IBC merge mode, and parses,from the coded video bitstream, a second flag that indicates whether thetemplate matching is applied to the block vector candidate of theplurality of IBC candidates in the IBC merge mode that is indicated bythe merge index.

In another example, the processing circuitry parses, from the codedvideo bitstream, a flag indicating the IBC merge mode, the templatematching being applied to a block vector candidate of each block in theCTU that is predicted in the IBC merge mode.

In some examples, the processing circuitry constructs the IBC mergecandidate list that includes at least a first block vector candidatethat points to a first position that is outside an IBC reference region.

In an example, the processing circuitry determines, in response to themerge index indicating the first block vector candidate, a closestposition in the IBC reference region to the first position, anddetermines the initial block vector to point to the closest position.

In an example, to construct the IBC merge candidate list, the processingcircuitry inserts the first block vector candidate into the IBC mergecandidate list in response to a determination that a template matchingsearch region of the first block vector candidate at least partiallyoverlaps with the IBC reference region.

In some examples, the IBC reference region includes a reconstructedportion of the current CTU and a region of a left CTU that are cached ina memory space of a size for storing a CTU.

In some examples, the processing circuitry excludes a portion of thetemplate matching search region that is out of the IBC reference regionfrom the template matching.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 9 shows an example of intra block copy according to an embodimentof the disclosure.

FIG. 10 shows an example of intra block copy according to an embodimentof the disclosure.

FIG. 11 shows an example of intra block copy according to an embodimentof the disclosure.

FIGS. 12A-12D show examples of intra block copy according to anembodiment of the disclosure.

FIG. 13 shows an example for template matching search in someembodiments.

FIG. 14 shows a table of search patterns for adaptive motion vectorresolution (AMVR) and merge mode in some examples.

FIG. 15 shows an example of pseudo codes for template matching in someembodiments.

FIG. 16 shows an example of prediction in the intra block copy modeaccording to an embodiment of the disclosure.

FIG. 17 shows a flow chart outlining a process according to someembodiment of the disclosure.

FIG. 18 shows a flow chart outlining another process according to someembodiment of the disclosure.

FIG. 19 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Block based compensation can be used for inter prediction and intraprediction. For the inter prediction, block based compensation from adifferent picture is known as motion compensation. Block basedcompensation can also be done from a previously reconstructed areawithin the same picture, such as in intra prediction. The block basedcompensation from reconstructed area within the same picture is referredto as intra picture block compensation, current picture referencing(CPR), or intra block copy (IBC). A displacement vector that indicatesan offset between a current block and a reference block (also referredto as a prediction block) in the same picture is referred to as a blockvector (BV) where the current block can be encoded/decoded based on thereference block. Different from a motion vector in motion compensation,which can be at any value (positive or negative, at either x or ydirection), a BV has a few constraints to ensure that the referenceblock is available and already reconstructed. Also, in some examples,for parallel processing consideration, some reference area that is tileboundary, slice boundary, or wavefront ladder shape boundary isexcluded.

In some examples, IBC mode can be used to significantly improve thecoding efficiency of screen content materials. Generally, IBC mode canbe implemented as a block level coding mode. At the encoder side, theencoder can perform block matching (BM) to find the optimal block vectorfor each CU. In some examples, at the encoder side, a hash-based motionestimation (also referred to as hash based search) is performed for a CUin the IBC mode. The encoder can perform rate distortion (RD) check forblocks with either width or height no larger than 16 luma samples. Fornon-merge mode, the block vector search is performed using hash-basedsearch first. If hash search does not return valid candidate, blockmatching based local search can be performed.

In some examples, in the hash-based search, hash key matching (32-bitCRC) between the current block and a reference block is extended to allallowed block sizes in the current picture. The hash key calculation forevery position in the current picture can be based on 4×4 subblocks. Forthe current block of a larger size, a hash key can be determined tomatch that of the reference block when all the hash keys of all 4×4subblocks match the hash keys in the corresponding reference locations.If hash keys of multiple reference blocks are found to match that of thecurrent block, the block vector costs of each of the matched referenceblocks can be calculated and the one matched reference block with theminimum cost is then selected as the result of the hash-based search.

In some examples, the block matching search searches a region that islocal to the current block. For example, in the block matching search,the search range is set to cover both the previous and current CTUs.

In some implementation examples, the resolution of a block vector isrestricted to integer positions. In some other systems, the block vectormay be allowed to point to fractional positions. In some examples, theluma block vector of an IBC coded CU is in integer precision. The chromablock vector can round to integer precision as well. In some examples,IBC mode can be combined with adaptive motion vector resolution (AMVR),and can switch between 1 pixel (pel) and 4-pel motion vector precisions.In some implementation examples, the IBC mode is treated as the thirdprediction mode other than intra or inter prediction modes. The IBC modeis applicable to the CUs with both width and height smaller than orequal to 64 luma samples in some examples.

The coding of a block vector could be either explicit or implicit. Inthe explicit mode, a BV difference between a block vector and itspredictor is signaled. In the implicit mode, the block vector isrecovered from a predictor (referred to as block vector predictor)without using the BV difference, in a similar way as a motion vector inthe merge mode. The explicit mode can be referred to as a non-merge BVprediction mode, or IBC AMVP mode in some examples. The implicit modecan be referred to as a merge BV prediction mode, IBC merge mode, IBCskip mode in some examples.

There can be variations for the IBC mode. In an example, the IBC mode istreated as a third mode that is different from the intra prediction modeand the inter prediction mode. Accordingly, the BV prediction in theimplicit mode (or the IBC merge mode) and the explicit mode (IBC AMVPmode) are separated from the regular inter mode. In some examples aseparate merge candidate list can be defined for the IBC mode whereentries in the separate merge candidate list are BVs. Similarly, in anexample, a BV prediction candidate list in the IBC explicit mode (IBCAMVP mode) only includes BVs. General rules applied to the two lists(i.e., the separate merge candidate list for IBC merge mode and the BVprediction candidate list for the IBC AMVP mode) are that the two listsmay follow the same logic as a merge candidate list used in the regularmerge mode (used in inter prediction) or an advanced motion vectorprediction (AMVP) predictor list used in the regular AMVP mode (used ininter prediction) in terms of the candidate derivation process. Forexample, the five spatial neighboring locations (e.g., A0, A1, and B0,B1, B2 in FIG. 2 ), for example, HEVC or VVC inter merge mode areaccessed for the IBC merge mode to derive the separate merge candidatelist for the IBC merge mode.

In an implementation example, for a CU, a block level flag is used tosignal whether IBC AMVP mode or IBC skip/merge mode is used. In anexample, when a flag (e.g., denoted merge_flag) is true, IBC skip/mergemode is used; and when the flag is false, IBC AMVP mode is used.

In some examples, for the IBC skip/merge mode, a merge candidate indexcan be signaled to indicate which of the block vectors in the mergecandidate list from neighboring candidate IBC coded blocks is used asthe BV predictor to predict the current block. The merge candidate listcan include spatial, history-based motion vector prediction (HMVP), andpairwise candidates in some examples.

In some examples, for the IBC AMVP mode, a block vector difference iscoded in the coded bitstream in the same way as a motion vectordifference. The block vector prediction in the IBC AMVP mode can use twocandidates as predictors, one from left neighbor and one from aboveneighbor (if IBC coded). When either neighbor is not available, adefault block vector can be used as a predictor. In an example, a flagis signaled in the coded bitstream to indicate the index of the BVpredictor.

As described above, a BV of a current block under reconstruction in apicture can have certain constraints, and thus, a reference block forthe current block is within an IBC reference region.

The IBC reference region refers to a part of the picture from which thereference block can be selected. For example, the IBC reference regionmay be within certain portions of a reconstructed area in the picture. Asize, a position, a shape, and/or the like of the IBC reference regioncan be constrained. Alternatively, the BV can be constrained. In anexample, the BV is a two-dimensional vector including an x and a ycomponent, and at least one of the x and y components can beconstrained. Constraints can be specified with respect to the BV, theIBC reference region, or a combination of the BV and the IBC referenceregion. In various examples, when certain constraints are specified withrespect to the BV, the IBC reference region is constrained accordingly.Similarly, when certain constraints are specified with respect to theIBC reference region, the BV is constrained accordingly.

FIG. 9 shows an example of intra block copy according to an embodimentof the disclosure. A current picture (900) is to be reconstructed underdecoding. The current picture (900) includes a reconstructed area (910)(grey area) and a to-be-decoded area (920) (white area). A current block(930) is under reconstruction by a decoder. The current block (930) canbe reconstructed from a reference block (940) that is in thereconstructed area (910). A position offset between the reference block(940) and the current block (930) is referred to as a block vector (950)(or BV (950)). In the FIG. 9 example, an IBC reference region (960) iswithin the reconstructed area (910), the reference block (940) is withinIBC reference region (960), and the block vector (950) is constrained topoint to the reference block (940) within the IBC reference region(960).

Various constraints can be applied to a BV and/or aN IBC referenceregion. In an embodiment, an IBC reference region for a current blockunder reconstruction in a current CTB is constrained to be within thecurrent CTB.

In an embodiment, an effective memory requirement to store referencesamples to be used in intra block copy is one CTB size. In an example,the CTB size is 128×128 samples. A current CTB includes a current regionunder reconstruction. The current region has a size of 64×64 samples.Since a reference memory can also store reconstructed samples in thecurrent region, the reference memory can store 3 more regions of 64×64samples when a reference memory size is equal to the CTB size of 128×128samples. Accordingly, an IBC reference region can include certain partsof a previously reconstructed CTB while a total memory requirement forstoring reference samples is unchanged (such as 1 CTB size of 128×128samples or 4 64×64 reference samples in total). In an example, thepreviously reconstructed CTB is a left neighbor of the current CTB, suchas shown in FIG. 10 .

FIG. 10 shows an example of intra block copy according to an embodimentof the disclosure. A current picture (1001) includes a current CTB(1015) under reconstruction and a previously reconstructed CTB (1010)that is a left neighbor of the current CTB (1015). CTBs in the currentpicture (1001) have a CTB size, such as 128×128 samples, and a CTBwidth, such as 128 samples. The current CTB (1015) includes 4 regions(1016)-(1019), where the current region (1016) is under reconstruction.The current region (1016) includes a plurality of coding blocks(1021)-(1029). Similarly, the previously reconstructed CTB (1010)includes 4 regions (1011)-(1014). The coding blocks (1021)-(1025) arereconstructed, the current block (1026) is under reconstruction, and thecoding blocks (1026)-(1027) and the regions (1017)-(1019) are to bereconstructed.

The current region (1016) has a collocated region (i.e., the region(1011), in the previously reconstructed CTB (1010)). A relative positionof the collocated region (1011) with respect to the previouslyreconstructed CTB (1010) can be identical to a relative position of thecurrent region (1016) with respect to the current CTB (1015). In theexample illustrated in FIG. 10 , the current region (1016) is a top leftregion in the current CTB (1015), and thus, the collocated region (1011)is also a top left region in the previously reconstructed CTB (1010).Since a position of the previously reconstructed CTB (1010) is offsetfrom a position of the current CTB (1015) by the CTB width, a positionof the collocated region (1011) is offset from a position of the currentregion (1016) by the CTB width.

In an embodiment, a collocated region of the current region (1016) is ina previously reconstructed CTB where a position of the previouslyreconstructed CTB is offset by one or multiples of the CTB width fromthe positon of the current CTB (1015), and thus, a position of thecollocated region is also offset by a corresponding one or multiples ofthe CTB width from the position of the current region (1016). Theposition of the collocated region can be left shifted, up shifted, orthe like from the current region (1016).

As described above, a size of the IBC reference region for the currentblock (1026) is constrained by the CTB size. In the FIG. 10 example, theIBC reference region can include the regions (1012)-(1014) in thepreviously reconstructed CTB (1010) and a portion of the current region(1016) that is already reconstructed, such as the coding blocks(1021)-(1025). The IBC reference region can exclude the collocatedregion (1011) so that the size of the search range is within the CTBsize. Referring to FIG. 10 , a reference block (1091) is located in theregion (1014) of the previously reconstructed CTB (1010). A block vector(1020) indicates an offset between the current block (1026) and therespective reference block (1091). The reference block (1091) is in theIBC reference region.

The example illustrated in FIG. 10 can be suitably adapted to otherscenarios where a current region is located at another location in thecurrent CTB (1015). In an example, when a current block is in the region(1017), a collocated region for the current block is the region (1012).Therefore, an IBC reference region can include the regions(1013)-(1014), the region (1016), and a portion of the region (1017)that is already reconstructed. The search range further excludes theregion (1011) and the collocated region (1012) so that the size of theIBC reference region is within the CTB size. In an example, when acurrent block is in the region (1018), a collocated region for thecurrent block is the region (1013). Therefore, an IBC reference regioncan include the region (1014), the regions (1016)-(1017), and a portionof the region (1018) that is already reconstructed. The IBC referenceregion further excludes the regions (1011)-(1012) and the collocatedregion (1013) so that the size of the IBC reference region is within theCTB size. In an example, when a current block is in the region (1019), acollocated region for the current block is the region (1014). Therefore,an IBC reference region can include the regions (1016)-(1018), and aportion of the region (1019) that is already reconstructed. The IBCreference region further excludes the previously reconstructed CTB(1010) so that the size of the IBC reference region is within the CTBsize.

In the above description, a reference block can be in the previouslyreconstructed CTB (1010) or the current CTB (1015).

In an embodiment, an IBC reference region can be specified as below. Inan example, a current picture is a luma picture and a current CTB is aluma CTB including a plurality of luma samples and a BV (mvL) satisfiesthe following constraints for bitstream conformance. In an example, theBV (mvL) has a fractional resolution (e.g., 1/16-pel resolution).

The constraints include first conditions that a reference block for thecurrent block is already reconstructed. When the reference block has arectangular shape, a neighboring block availability checking process (ora reference block availability checking process) can be implemented tocheck whether a top left sample and a bottom right sample of thereference block are reconstructed. When both the top left sample and thebottom right sample of the reference block are reconstructed, thereference block is determined to be reconstructed.

For example, when a derivation process for reference block availabilityis invoked with a position (xCurr, yCurr) of a top left sample of thecurrent block set to be (xCb, yCb) and a position (xCb+(mvL[0]>>4),yCb+(mvL[1]>>4)) of the top left sample of the reference block asinputs, an output is equal to TRUE when the top left sample of thereference block is reconstructed where the block vector mvL is atwo-dimensional vector having a x component mvL[0] and a y componentmvL[1]. When the BV (mvL) has a fractional resolution, such as 1/16-pelresolution, the x component mvL[0] and the y component mvL[1] areshifted to have an integer resolution, as indicated by mvL[0]>>4 andmvL[1]>>4, respectively.

Similarly, when a derivation process for block availability is invokedwith the position (xCurr, yCurr) of the top left sample of the currentblock set to be (xCb, yCb) and a position (xCb+(mvL[0]>>4)+cbWidth−1,yCb+(mvL[1]>>4)+cbHeight−1) of the bottom right sample of the referenceblock as inputs, an output is equal to TRUE when the bottom right sampleof the reference block is reconstructed. The parameters cbWidth andcbHeight represent a width and a height of the reference block.

The constraints can also include at least one of the following secondconditions: 1) a value of (mvL[0]>>4)+cbWidth is less than or equal to0, which indicates that the reference block is to the left of thecurrent block and does not overlap with the current block; 2) a value of(mvL[1]>>4)+cbHeight is less than or equal to 0, which indicates thatthe reference block is above the current block and does not overlap withthe current block.

The constraints can also include that the following third conditions aresatisfied by the block vector mvL:

(yCb+(mvL[1]>>4))>>CtbLog2SizeY=yCb>>CtbLog2SizeY  (1)

(yCb+(mvL[1]>>4+cbHeight−1)>>CtbLog2SizeY=yCb>>CtbLog2Size  (2)

(xCb+(mvL[0]>>4))>>CtbLog2SizeY>=(xCb>>CtbLog2SizeY)−1  (3)

(xCb+(mvL[0]>>4)+cbWidth−1)>>CtbLog2SizeY(xCb>>CtbLog2SizeY)  (4)

where the parameters CtbLog2SizeY represents the CTB width in log2 form.For example, when the CTB width is 128 samples, CtbLog2SizeY is 7. Eqs.(1)-(2) specify that a CTB including the reference block is in a sameCTB row as the current CTB (e.g., the previously reconstructed CTB(1010) is in a same row as the current CTB (1015) when the referenceblock is in the previously reconstructed CTB (1010)). Eqs. (3)-(4)specify that the CTB including the reference block is either in a leftCTB column of the current CTB or a same CTB column as the current CTB.The third conditions as described by Eqs. (1)-(4) specify that the CTBincluding the reference block is either the current CTB, such as thecurrent CTB (1015), or a left neighbor, such as the previouslyreconstructed CTB (1010), of the current CTB, similarly to thedescription with reference to FIG. 10 .

The constraints can further include fourth conditions: when thereference block is in the left neighbor of the current CTB, a collocatedregion for the reference block is not reconstructed (i.e., no samples inthe collocated region have been reconstructed). Further, the collocatedregion for the reference block is in the current CTB. In the FIG. 10example, a collocated region for the reference block (1091) is theregion (1019) that is offset by the CTB width from the region (1014)where the reference block (1091) is located and the region (1019) hasnot been reconstructed. Therefore, the block vector (1020) and thereference block (1091) satisfy the fourth conditions described above.

In an example, the fourth conditions can be specified as below: when(xCb+(mvL[0]>>4))>>CtbLog2SizeY is equal to (xCb>>CtbLog2SizeY)−1, thederivation process for reference block availability is invoked with theposition of the current block (xCurr, yCurr) set to be (xCb, yCb) and aposition(((xCb+(mvL[0]>>4)+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1),((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)) as inputs, anoutput is equal to FALSE indicating that the collocated region is notreconstructed, such as shown in FIG. 10 .

The constraints for the IBC reference region and/or the block vector caninclude a suitable combination of the first, second, third, and fourthconditions described above. In an example, the constraints include thefirst, second, third, and fourth conditions, such as shown in FIG. 10 .In an example, the first, second, third, and/or fourth conditions can bemodified and the constraints include the modified first, second, third,and/or fourth conditions.

According to the fourth conditions, when one of the coding blocks(1022)-(1029) is a current block, a reference block cannot be in theregion (1011), and thus, an IBC reference region for the one of thecoding blocks (1022)-(1029) excludes the region (1011). The reasons whythe region (1011) is excluded are specified below: if the referenceblock is in the region (1011), then a collocated region for thereference block is the region (1016), however, at least samples in thecoding block (1021) have been reconstructed, and thus, the fourthconditions are violated. On the other hand, for a coding block to bereconstructed first in a current region, such as a coding block (1121)in a region (1116) in FIG. 11 , the fourth conditions does not prevent areference block to be in the region (1111) because a collocated region(1116) for the reference block has not been reconstructed yet.

FIG. 11 shows an example of intra block copy according to an embodimentof the disclosure. A current picture (1101) includes a current CTB(1115) under reconstruction and a previously reconstructed CTB (1110)that is a left neighbor of the current CTB (1115). CTBs in the currentpicture (1101) have a CTB size and a CTB width. The current CTB (1115)includes 4 regions (1116)-(1119) where the current region (1116) isunder reconstruction. The current region (1116) includes a plurality ofcoding blocks (1121)-(1129). Similarly, the previously reconstructed CTB(1110) includes 4 regions (1111)-(1114). The current block (1121) underreconstruction is to be reconstructed first in the current region (1116)and the coding blocks (1122)-(1129) are to be reconstructed. In anexample, the CTB size is 128×128 samples, each of the regions(1111)-(1114) and (1116)-(1119) is 64×64 samples. A reference memorysize is equal to the CTB size and is 128×128 samples, and thus, the IBCreference region, when bounded by the reference memory size, includes 3regions and a portion of an additional region.

Similarly as described with reference to FIG. 10 , the current region(1116) has a collocated region (i.e., the region (1111) in thepreviously reconstructed CTB (1110)). According to the fourth conditionsdescribed above, a reference block for the current block (1121) can bein the region (1111), and thus, an IBC reference region can include theregions (1111)-(1114). For example, when the reference block is in theregion (1111), a collocated region of the reference block is the region(1116), where no samples in the region (1116) have been reconstructedprior to the reconstruction of the current block (1121). However, asdescribed with reference to FIG. 10 and the fourth conditions, forexample, after the reconstruction of the coding block (1121), the region(1111) is no longer available to be included in an IBC reference regionfor reconstructing the coding block (1122). Therefore, a tightsynchronization and timing control of the reference memory buffer is tobe used and can be challenging.

According to some embodiments, when a current block is to bereconstructed first in a current region of a current CTB, an IBCreference region can exclude a collocated region of the current regionthat is in a previously reconstructed CTB where the current CTB and thepreviously reconstructed CTB are in a same current picture. A blockvector can be determined such that a reference block is in the IBCreference region that excludes the collocated region in the previouslyreconstructed CTB. In an embodiment, the IBC reference region includescoding blocks that are reconstructed after the collocated region andbefore the current block in a decoding order.

In the descriptions below, a CTB size can vary and a maximum CTB size isset to be identical to a reference memory size. In an example, thereference memory size or the maximum CTB size is 128×128 samples. Thedescriptions can be suitably adapted to other reference memory sizes ormaximum CTB sizes.

In an embodiment, the CTB size is equal to the reference memory size.The previously reconstructed CTB is a left neighbor of the current CTB,a position of the collocated region is offset by a CTB width from aposition of the current region, and the coding blocks in the IBCreference region are in at least one of: the current CTB and thepreviously reconstructed CTB.

FIGS. 12A-12D show examples of intra block copy according to anembodiment of the disclosure. Referring to FIGS. 12A-D, a currentpicture (1201) includes a current CTB (1215) under reconstruction and apreviously reconstructed CTB (1210) that is a left neighbor of thecurrent CTB (1215). CTBs in the current picture (1201) have a CTB sizeand a CTB width. The current CTB (1215) includes 4 regions(1216)-(1219). Similarly, the previously reconstructed CTB (1210)includes 4 regions (1211)-(1214). In an embodiment, the CTB size is amaximum CTB size and is equal to a reference memory size. In an example,the CTB size and the reference memory size are 128 by 128 samples, andthus, each of the regions (1211)-(1214) and (1216)-(1219) has a size of64 by 64 samples.

In the examples illustrated in FIGS. 12A-D, the current CTB (1215)includes a top left region, a top right region, a bottom left region,and a bottom right region that correspond to the regions (1216)-(1219),respectively. The previously reconstructed CTB (1210) includes a topleft region, a top right region, a bottom left region, and a bottomright region that correspond to the regions (1211)-(1214), respectively.

Referring to FIG. 12A, the current region (1216) is underreconstruction. The current region (1216) can include a plurality ofcoding blocks (1221)-(1229). The current region (1216) has a collocatedregion, i.e., the region (1211), in the previously reconstructed CTB(1210). An IBC reference region for one of the coding blocks(1221)-(1229) to be reconstructed can exclude the collocated region(1211). The IBC reference region can include the regions (1212)-(1214)of the previously reconstructed CTB (1210) that are reconstructed afterthe collocated region (1211) and before the current region (1216) in adecoding order.

Referring to FIG. 12A, a position of the collocated region (1211) isoffset by the CTB width, such as 128 samples, from a position of thecurrent region (1216). For example, the position of the collocatedregion (1211) is left shifted by 128 samples from the position of thecurrent region (1216).

Referring again to FIG. 12A, when the current region (1216) is the topleft region of the current CTB (1215), the collocated region (1211) isthe top left region of the previously reconstructed CTB (1210), and thesearch region excludes the top left region of the previouslyreconstructed CTB.

As shown in FIG. 12A, current block falls into the top-left 64×64 block(e.g., the current region (1216)) of the current CTU (e.g., shown by CTB(1215)), then in addition to the already reconstructed samples in thecurrent CTU (shown by CTB (1215)), samples in the bottom-right 64×64blocks (e.g., shown by (1214)) of the left CTU (e.g., shown by CTB(1210) can be referred to as reference samples for example using currentpicture referencing (CPR) mode. The current block can also refer to thesamples in the bottom-left 64×64 block (e.g., shown by (1213)) of theleft CTU (e.g., shown by CTB (1210)) and the samples in the top-right64×64 block (e.g., shown by (1212)) of the left CTU (e.g., shown by CTB(1210), using CPR mode.

Referring to FIG. 12B, the current region (1217) is underreconstruction. The current region (1217) can include a plurality ofcoding blocks (1241)-(1249). The current region (1217) has a collocatedregion (i.e., the region (1212), in the previously reconstructed CTB(1210)). An IBC reference region for one of the plurality of codingblocks (1241)-(1249) can exclude the collocated region (1212). The IBCreference region includes the regions (1213)-(1214) of the previouslyreconstructed CTB (1210) and the region (1216) in the current CTB (1215)that are reconstructed after the collocated region (1212) and before thecurrent region (1217). The IBC reference region further excludes theregion (1211) due to constraint of the reference memory size (i.e., oneCTB size). Similarly, a position of the collocated region (1212) isoffset by the CTB width, such as 128 samples, from a position of thecurrent region (1217).

In the FIG. 12B example, the current region (1217) is the top rightregion of the current CTB (1215), the collocated region (1212) is alsothe top right region of the previously reconstructed CTB (1210), and thesearch region excludes the top right region of the previouslyreconstructed CTB (1210).

As shown in FIG. 12B, if current block falls into the top-right 64×64block (e.g., shown by (1217) of the current CTU (e.g., shown by CTB(1215)), then in addition to the already reconstructed samples (e.g.,shown by (1216)) in the current CTU, if luma location (0, 64) relativeto the current CTU has not yet been reconstructed, the current block canalso refer to the samples in the bottom-left 64×64 block (e.g., shown as(1213)) and bottom-right 64×64 block (e.g., shown as (1214)) of the leftCTU, using CPR mode; otherwise, the current block can also refer toreference samples in bottom-right 64×64 block (e.g., shown as (1214)) ofthe left CTU.

Referring to FIG. 12C, the current region (1218) is underreconstruction. The current region (1218) can include a plurality ofcoding blocks (1261)-(1269). The current region (1218) has a collocatedregion (i.e., the region (1213)), in the previously reconstructed CTB(1210). An IBC reference region for one of the plurality of codingblocks (1261)-(1269) can exclude the collocated region (1213). The IBCreference region includes the region (1214) of the previouslyreconstructed CTB (1210) and the regions (1216)-(1217) in the currentCTB (1215) that are reconstructed after the collocated region (1213) andbefore the current region (1218). Similarly, the IBC reference regionfurther excludes the regions (1211)-(1212) due to constraint of thereference memory size. A position of the collocated region (1213) isoffset by the CTB width, such as 128 samples, from a position of thecurrent region (1218). In the FIG. 12C example, when the current region(1218) is the bottom left region of the current CTB (1215), thecollocated region (1213) is also the bottom left region of thepreviously reconstructed CTB (1210), and the search region excludes thebottom left region of the previously reconstructed CTB (1210).

As shown in FIG. 12C, if current block falls into the bottom-left 64×64block (e.g., shown by (1218)) of the current CTU (e.g., shown by CTB(1215)), then in addition to the already reconstructed samples (e.g.,(1216) and (1217)) in the current CTU, if luma location (64, 0) relativeto the current CTU has not yet been reconstructed, the current block canalso refer to the samples in the bottom-right 64×64 block (e.g., shownby (1214)) of the left CTU, using CPR mode.

Referring to FIG. 12D, the current region (1219) is underreconstruction. The current region (1219) can include a plurality ofcoding blocks (1281)-(1289). The current region (1219) has a collocatedregion (i.e., the region (1214)), in the previously reconstructed CTB(1210). A IBC reference region for one of the plurality of coding blocks(1281)-(1289) can exclude the collocated region (1214). The IBCreference region includes the regions (1216)-(1218) in the current CTB(1215) that are reconstructed after the collocated region (1214) andbefore the current region (1219) in a decoding order. The IBC referenceregion excludes the regions (1211)-(1213) due to constraint of thereference memory size, and thus, the IBC reference region excludes thepreviously reconstructed CTB (1210). Similarly, a position of thecollocated region (1214) is offset by the CTB width, such as 128samples, from a position of the current region (1219). In the FIG. 12Dexample, when the current region (1219) is the bottom right region ofthe current CTB (1215), the collocated region (1214) is also the bottomright region of the previously reconstructed CTB (1210) and the searchregion excludes the bottom right region of the previously reconstructedCTB (1210).

In FIG. 12D, current block falls into the bottom-right 64×64 block(shown by (1219)) of the current CTU, it can only refer to the alreadyreconstructed samples (e.g., (1216), (1217 and (1218) in the currentCTU, using CPR mode.

Using the restriction shown in FIG. 12A-12D, the IBC mode can beimplemented using local on-chip memory for hardware implementations insome examples.

According to an aspect of the disclosure, template matching (TM) searchrefers to decoder-side MV derivation techniques to refine the motioninformation of the current CU by finding the closest match between atemplate (i.e., top and/or left neighboring blocks of the current CU) inthe current picture and a block (i.e., same size to the template, and isreferred to as reference template) in a reference picture.

FIG. 13 shows an example for template matching search in someembodiments. In the FIG. 13 example, a current picture (1310) includes acurrent CU under reconstruction, the current template for the current CUincludes an above block and a left block that are neighboring to thecurrent CU. The above block and the left block form a current templatefor the current CU. In a reference picture (1320) for the currentpicture (1310), an initial motion vector (MV) points to a referencelocation, and a search region (1350) is defined as a region within [−8pel, +8 pel] of the reference location in X and Y direction.

In an example, a template matching search is used to search a better MVin the search region (1350) that has a closest match between thereference template and the current template. In some examples, thetemplate matching techniques can use search step size that is determinedbased on AMVR mode and template matching search can be cascaded withbilateral matching process in merge modes.

In some examples, in AMVP mode, a motion vector predictor (MVP)candidate is selected from a list of candidates based on template errorcalculation that can select the MVP candidate with a minimum differencebetween the current template and the reference template. Then templatematching search is performed based on this particular MVP candidate forMV refinement. In some examples, template matching search refines thisMVP candidate, starting from full-pel motion vector difference (MVD)precision (or 4-pel for 4-pel AMVR mode) within a [−8, +8]-pel searchrange by using an iterative diamond search pattern. The AMVP candidatemay be further refined by using cross search pattern with full-pel MVDprecision (or 4-pel for 4-pel AMVR mode), followed sequentially byhalf-pel cross search pattern and quarter-pel cross search patterndepending on AMVR mode. This search process ensures that the MVPcandidate keeps the same MV precision as indicated by the AMVR modeafter TM search process.

FIG. 14 shows a table (1400) of search patterns for AMVR and merge modein some examples.

In some examples, in the merge mode, similar search method is applied tothe merge candidate indicated by the merge index. As shown in the tablein FIG. 14 , TM search may perform all the way down to 1/8-pel MVDprecision or skipping those beyond half-pel MVD precision, depending onwhether the alternative interpolation filter (that is used when AMVR isof half-pel mode) is used according to merged motion information. Forexample, a variable AltIF being 0 indicates that alternativeinterpolation filter is not used, and the TM search may perform all theway down to 1/8-pel MVD precision; and the variable AltIF being 1indicates that the alternative interpolation filter is used, and TMsearch may perform to half-pel precision. Besides, when TM mode isenabled, template matching may work as an independent process or anextra MV refinement process between block-based and subblock-basedbilateral matching methods, depending on whether bilateral matching canbe enabled or not according to enabling condition check.

According to some aspects of the disclosure, the template matchingtechniques can be used in the IBC mode to perform template matchingsearch based on IBC merge candidates to achieve block vectorrefinements.

According to an aspect of the disclosure, for merge candidate list inthe IBC mode, only a certain number of candidates can be on the mergecandidate list and the merge index is signaled to indicate one in themerge candidate list. However, using template matching method, decodermay be able to derive the best block vector by searching the close blockvector based on the templates. Furthermore, while constructing IBC mergecandidate list, candidate BVs which are outside of IBC reference regionsare considered invalid and the invalid candidate BVs are removed fromthe merge candidate list. However, there exist cases that the best BVcomes from those invalid candidate BVs.

Some aspects of the disclosure provide techniques that allow invalid BVsin the merge candidate list, and template matching search can beperformed based on the invalid BVs to achieve better BV (e.g., lesstemplate error) in the IBC mode.

In an embodiment, a flag can be used to indicate whether templatematching is applied to IBC merge candidates.

FIG. 15 shows an example of pseudo codes (1500) for template matching insome embodiments.

In the FIG. 15 example, when the current block (PU) is in the IBC mode,a first flag (e.g., denoted by merge_flag) is in signaled in the codedbitstream to indicate whether the current block is coded in IBC AMVPmode, or IBC merge mode. The first flag can be parsed from thebitstream, as shown by (1501) in FIG. 15 . When the first flag(merge_flag) is equal to 1, the current block is coded using IBC mergemode. When the current block is in the IBC merge mode, a second flag(e.g., denoted by template_matching_ibc_merge_flag) and a merge index(e.g., denoted by merge_idx) are signaled in the coded bitstream. Thesecond flag can be parsed from the coded bitstream as shown by (1502) inFIG. 15 , and the merge index can be parsed from the coded bitstream asshown by (1503) in FIG. 15 .

The merge index indicates a candidate BV in the IBC merge candidatelist. When the second flag (e.g., template_matching_ibc_merge_flag)equals to 1, template matching search can be performed using thecandidate BV that is indicated by the merge index in the IBC mergecandidate list as an initial BV. When the second flag(template_matching_ibc_merge_flag) equals 0, in an example, templatematching search is disabled, and the candidate BV that is indicated bythe merge index is used as the block vector that points to a referenceblock to reconstruct the current block (current PU).

In some embodiments, template matching search is tied with the IBC mergemode. Thus, the template matching search can be applied in IBC mergemode without signaling the second flag (e.g.,template_matching_ibc_merge_flag). The merge index can be signaled toindicate a candidate BV from the IBC merge candidate list to be used asan initial BV for the template matching.

According to another aspect of the disclosure, during construction ofthe IBC merge candidate list, in the process of checking validity ofeach IBC merge candidate, instead using solely the IBC reference region,a template matching search range (Sr) is taking into account with theIBC reference region.

FIG. 16 shows an example of IBC according to an embodiment of thedisclosure. In FIG. 16 a current picture (1601) includes a current CTB(1615) under reconstruction and a previously reconstructed CTB (1610)that is a left neighbor of the current CTB (1615). The current CTB(1615) includes 4 regions (1616)-(1619). Similarly, the previouslyreconstructed CTB (1610) includes 4 regions (1611)-(1614). In anembodiment, the CTB size is a maximum CTB size and is equal to areference memory size. In an example, the CTB size and the referencememory size are 128 by 128 samples, and thus, each of the regions(1611)-(1614) and (1616)-(1619) has a size of 64 by 64 samples.

In the FIG. 16 example, the current region (1616) is underreconstruction. The current region (1616) has a collocated region, i.e.,the region (1611), in the previously reconstructed CTB (1610). An IBCreference region for a current block (1650) to be reconstructed canexclude the collocated region (1611). The IBC reference region caninclude the regions (1612)-(1614) of the previously reconstructed CTB(1610) that are reconstructed after the collocated region (1611) andbefore the current region (1616) in a decoding order.

In the FIG. 16 example, an arrow (1651) indicates a candidate BV in theIBC merge candidate list. The candidate BV points to a position A. Arectangular box (1652) around the position A is the template matchingsearch range that can be denoted by Sr. In an example, the position Ahas a 2-dimensional coordinate (x0, y0). Then, the rectangular box(1652) can be defined by four corners of (x0−Sr, y0−Sr), (x0+Sr, y0−Sr),(x0−Sr, y0+Sr), and (x0+Sr, y0+Sr). In some related examples, thecandidate BV (1651) is considered invalid and is not put in the IBCmerge candidate list, because the position A is outside of IBC referenceregion (the region (1611) is excluded from the IBC reference region).

In some embodiments, invalid merge candidates, such as the candidate BV(1651) can be inserted in the IBC merge candidate list. To performtemplate matching search based on the candidate BV (1651), the positionA (that is pointed by the candidate BV (1651) is moved into the IBCreference range, for example, to the position C that is the closestposition inside valid IBC reference range to the position A. Then,template matching search can start further searching and refinementwithin template matching searching range from the position C. In theFIG. 16 example, if a top left corner B of the region (1612) has 2Dcoordinates of (x1, y1), then the position C can has 2D coordinates of(x1, y0) in an example.

In some embodiments, during the validate checking of the IBC mergecandidates, a candidate BV is considered as valid when the templatematching search range of the BV is partially or fully collocated withthe IBC reference region. In the FIG. 16 example, the template matchingsearch region (1652) for the candidate BV (1651) partially overlaps withthe IBC reference region (including the region (1612), the region(1613), the region (1614)), thus the candidate BV (1651) is consideredvalid, and can be put in the IBC merge candidate list. In anotherexample, if x0+Sr>x1, the candidate BV (1651) is valid. Similarly, ify0+Sr>y1, the candidate BV (1651) is valid.

Further, according to an aspect of the disclosure, during the templatematching search, when an intermediate block vector is outside the IBCreference region, the intermediate block vector is not considered, andtemplate matching calculations (e.g., difference calculation of thecurrent template and the reference template pointed by the intermediateblock vector) associated with intermediate block vector can be skipped.

FIG. 17 shows a flow chart outlining a process (1700) according to anembodiment of the disclosure. The process (1700) can be used in a videoencoder. In various embodiments, the process (1700) is executed byprocessing circuitry, such as the processing circuitry in the terminaldevices (310), (320), (330) and (340), the processing circuitry thatperforms functions of the video encoder (403), the processing circuitrythat performs functions of the video encoder (603), the processingcircuitry that performs functions of the video encoder (703), and thelike. In some embodiments, the process (1700) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1700). Theprocess starts at (S17301) and proceeds to (S1710).

At (S1710), an initial block vector for predicting a current block in acurrent coding tree unit (CTU) is determined when the current block isin the IBC mode.

At (S1720), a template matching search is performed based on the initialblock vector to determine a refined block vector that points to areference block in a same picture as the current block.

At (S1730), a reconstructed current block is generated based on thereference block.

At (S1740), a coded video bitstream that carries the picture is encodedto include information indicative of the initial block vector.

In some examples, a merge index that indicates a block vector candidatefrom a merge candidate list is encoded in the coded video bitstream, andthe initial block vector is determined based on the block vectorcandidate. In some examples, the block vector candidate is determined bythe encoder using at least one of block matching or hash-based motionestimation.

In an example, a first flag indicative of an IBC merge mode is encodedin the coded video bitstream, and a second flag that indicates toperform the template matching search is encoded in the coded videobitstream.

In another example, a first flag indicative of an IBC merge mode and toperform the template matching search encoding is encoded in the codedvideo bitstream.

In some embodiments, the merge candidate list is configured to includeat least a first block vector candidate that points to a first positionthat is outside an IBC reference region. In an example, to determine theinitial block vector based on the first block vector candidate, aclosest position in the IBC reference region to the first position isdetermined; and the initial block vector is determined to point to theclosest position.

In some embodiments, to construct the merge candidate list, the firstblock vector candidate is inserted into the merge candidate list inresponse to a determination that a template matching search region ofthe first block vector candidate overlaps with the IBC reference region.

In some examples, the IBC reference region includes a reconstructedportion of the current CTU and a region of a left CTU that are cached ina memory space of a size for storing a CTU.

In some examples, to perform the template matching search, a portion ofthe template matching search region that is out of the IBC referenceregion is excluded from the template matching search.

Then, the process proceeds to (S1799) and terminates.

The process (1700) can be suitably adapted. Step(s) in the process(1700) can be modified and/or omitted. Additional step(s) can be added.Any suitable order of implementation can be used.

FIG. 18 shows a flow chart outlining a process (1800) according to anembodiment of the disclosure. The process (1800) can be used in a videodecoder. In various embodiments, the process (1800) is executed byprocessing circuitry, such as the processing circuitry in the terminaldevices (310), (320), (330) and (340), the processing circuitry thatperforms functions of the video decoder (410), the processing circuitrythat performs functions of the video decoder (510), and the like. Insome embodiments, the process (1800) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1800). Theprocess starts at (S1801) and proceeds to (S1810).

At (S1810), an initial block vector for predicting a current block in acurrent coding tree unit (CTU) is determined when the current block isin an IBC mode.

At (S1820), a template matching search is performed based on the initialblock vector to determine a refined block vector that points to areference block in a same picture as the current block.

At (S1830), a reconstructed current block is generated based on thereference block.

In some examples, the initial block vector is determined from a codedvideo bitstream that carries the picture based on a merge index. Themerge index indicates, from a merge candidate list, a block vectorcandidate.

In an example, a first flag indicative of an IBC merge mode is parsedfrom the coded video bitstream. Then, a second flag that indicates toperform the template matching search is parsed, from the coded videobitstream.

In another example, a flag indicative of an IBC merge mode and toperform the template matching search is parsed, from the coded videobitstream that carries the picture.

In some examples, the merge candidate list is constructed to include atleast a first block vector candidate that points to a first positionthat is outside an IBC reference region. In response to the merge indexindicating the first block vector candidate, a closest position in theIBC reference region to the first position is determined and the initialblock vector is determined to point to the closest position.

In some examples, to construct the merge candidate list, the first blockvector candidate is inserted into the merge candidate list in responseto a determination that a template matching search region of the firstblock vector candidate overlaps with the IBC reference region.

In some examples, to perform the template matching search, a portion ofthe template matching search region that is out of the IBC referenceregion is excluded from the template matching search.

In some examples, the IBC reference region includes a reconstructedportion of the current CTU and a region of a left CTU that are cached ina memory space of a size for storing a CTU.

Then, the process proceeds to (S1899) and terminates.

The process (1800) can be suitably adapted. Step(s) in the process(1800) can be modified and/or omitted. Additional step(s) can be added.Any suitable order of implementation can be used.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 19 shows a computersystem (1900) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 19 for computer system (1900) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1900).

Computer system (1900) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1901), mouse (1902), trackpad (1903), touchscreen (1910), data-glove (not shown), joystick (1905), microphone(1906), scanner (1907), camera (1908).

Computer system (1900) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1910), data-glove (not shown), or joystick (1905), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1909), headphones(not depicted)), visual output devices (such as screens (1910) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1900) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1920) with CD/DVD or the like media (1921), thumb-drive (1922),removable hard drive or solid state drive (1923), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1900) can also include an interface (1954) to one ormore communication networks (1955). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (1949) (such as,for example USB ports of the computer system (1900)); others arecommonly integrated into the core of the computer system (1900) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (1900) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1940) of thecomputer system (1900).

The core (1940) can include one or more Central Processing Units (CPU)(1941), Graphics Processing Units (GPU) (1942), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1943), hardware accelerators for certain tasks (1944), graphicsadapters (1950), and so forth. These devices, along with Read-onlymemory (ROM) (1945), Random-access memory (1946), internal mass storagesuch as internal non-user accessible hard drives, SSDs, and the like(1947), may be connected through a system bus (1948). In some computersystems, the system bus (1948) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (1948), or through a peripheral bus (1949). In anexample, the screen (1910) can be connected to the graphics adapter(1950). Architectures for a peripheral bus include PCI, USB, and thelike.

CPUs (1941), GPUs (1942), FPGAs (1943), and accelerators (1944) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1945) or RAM (1946). Transitional data can be also be stored in RAM(1946), whereas permanent data can be stored for example, in theinternal mass storage (1947). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1941), GPU (1942), massstorage (1947), ROM (1945), RAM (1946), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1900), and specifically the core (1940) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1940) that are of non-transitorynature, such as core-internal mass storage (1947) or ROM (1945). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1940). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1940) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1946) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1944)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

Appendix A: Acronyms

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video processing in a decoder,comprising: determining, by a processor, an initial block vector forpredicting a current block in a current coding tree unit (CTU) inresponse to the current block being predicted in an intra block copy(IBC) mode; performing, by the processor, template matching based on theinitial block vector to determine a refined block vector that points toa reference block in a picture as the current block; and reconstructing,by the processor, the current block based on the reference block.
 2. Themethod of claim 1, further comprising: determining the initial blockvector based on a merge index included in a coded video bitstream,wherein the merge index indicates a block vector candidate in an IBCmerge candidate list including a plurality of IBC candidates in an IBCmerge mode.
 3. The method of claim 2, further comprising: parsing, fromthe coded video bitstream, a first flag indicative of the IBC mergemode; and parsing, from the coded video bitstream, a second flag thatindicates whether the template matching is applied to the block vectorcandidate of the plurality of IBC candidates in the IBC merge mode thatis indicated by the merge index.
 4. The method of claim 2, furthercomprising: parsing, from the coded video bitstream, a flag indicatingthe IBC merge mode, the template matching being applied to a blockvector candidate of each block in the CTU that is predicted in the IBCmerge mode.
 5. The method of claim 2, further comprising: constructing,the IBC merge candidate list that includes at least a first block vectorcandidate that points to a first position that is outside an IBCreference region.
 6. The method of claim 5, wherein the determining theinitial block vector based on the merge index further comprises:determining, in response to the merge index indicating the first blockvector candidate, a closest position in the IBC reference region to thefirst position; and determining the initial block vector to point to theclosest position.
 7. The method of claim 5, wherein the constructing theIBC merge candidate list further comprises: inserting the first blockvector candidate into the IBC merge candidate list in response to adetermination that a template matching search region of the first blockvector candidate at least partially overlaps with the IBC referenceregion.
 8. The method of claim 5, wherein the IBC reference regionincludes a reconstructed portion of the current CTU and a region of aleft CTU that are cached in a memory space of a size for storing a CTU.9. The method of claim 7, wherein the performing the template matchingfurther comprises: excluding a portion of the template matching searchregion that is out of the IBC reference region from the templatematching.
 10. An apparatus for video decoding, comprising processingcircuitry configured to: determine an initial block vector forpredicting a current block in a current coding tree unit (CTU) inresponse to the current block being predicted in an intra block copy(IBC) mode; perform template matching based on the initial block vectorto determine a refined block vector that points to a reference block ina picture as the current block; and reconstructing the current blockbased on the reference block.
 11. The apparatus of claim 10, wherein theprocessing circuitry is configured to: determine, the initial blockvector based on a merge index included in a coded video bitstream,wherein the merge index indicates a block vector candidate in an IBCmerge candidate list including a plurality of IBC candidates in an IBCmerge mode.
 12. The apparatus of claim 11, wherein the processingcircuitry is configured to: parse, from the coded video bitstream thatcarries the picture, a first flag indicative of the IBC merge mode; andparse, from the coded video bitstream, a second flag that indicateswhether the template matching is applied to the block vector candidateof the plurality of IBC candidates in the IBC mode that is indicated bythe merge index.
 13. The apparatus of claim 11, wherein the processingcircuitry is configured to: parse, from the coded video bitstream thatcarries the picture, a flag indicating the IBC merge mode, the templatematching being applied to a block vector candidate of each block in theCTU that is predicted in the IBC merge mode.
 14. The apparatus of claim11, wherein the processing circuitry is configured to: construct, theIBC merge candidate list that includes at least a first block vectorcandidate that points to a first position that is outside an IBCreference region.
 15. The apparatus of claim 14, wherein the processingcircuitry is configured to: determine, in response to the merge indexindicating the first block vector candidate, a closest position in theIBC reference region to the first position; and determine the initialblock vector to point to the closest position.
 16. The apparatus ofclaim 14, wherein the processing circuitry is configured to: insert thefirst block vector candidate into the IBC merge candidate list inresponse to a determination that a template matching search region ofthe first block vector candidate at least partially overlaps with theIBC reference region.
 17. The apparatus of claim 14, wherein the IBCreference region includes a reconstructed portion of the current CTU anda region of a left CTU that are cached in a memory space of a size forstoring a CTU.
 18. The apparatus of claim 16, wherein the processingcircuitry is configured to: exclude a portion of the template matchingsearch region that is out of the IBC reference region from the templatematching.
 19. A non-transitory computer-readable storage medium storinginstructions which when executed by at least one processor cause the atleast one processor to perform: determining an initial block vector forpredicting a current block in a current coding tree unit (CTU) inresponse to the current block being predicted in an intra block copy(IBC) mode; performing a template matching based on the initial blockvector to determine a refined block vector that points to a referenceblock in a picture as the current block; and reconstructing the currentblock based on the reference block.
 20. The non-transitorycomputer-readable storage medium of claim 19, wherein the instructionscause the at least one processor to perform: constructing, an IBC mergecandidate list that includes at least a first block vector candidatethat points to a first position that is outside an IBC reference region;and determining, the initial block vector based on a merge index parsedfrom a coded video bitstream that carries the picture.